Apparatus for removing particulate matter

ABSTRACT

An apparatus for removing particulate matter is provided which is able to lower a temperature to burn particulate matter. The apparatus for removing particulate matter burns and removes the particulate matter emitted from an internal combustion engine, and comprises a perovskite-type complex oxide which is represented by the general formula ABO 3  where B is a metal having a valence of +3 or more. The metal having a valence of +3 or more for B of the general formula comprises at least one metal selected from the group consisting of Ti, Zr, Hf, V, Cr, Mo, W, Mn, Fe, Ru, Co, Ni, Cu, Ag, and Au. The perovskite-type complex oxide comprises at least one complex oxide selected from the group consisting of LaMn(III)O 3 , LaSrMn(III)O 3 , and LaCo(III)O 3 . The perovskite-type complex oxide supports Pt or Pd.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for removing particulatematter which burns and removes particulate matter emitted from aninternal combustion engine.

2. Description of the Related Art

Conventionally, an oxidizing catalyst has been used, which is a mixtureof refractory support such as alumina supporting a noble metal andoxygen storing material such as cerium oxide (ceria) for promotingoxidation, in order to purify harmful gases such as carbon monoxide(CO), hydrocarbon (HC) and nitrogen oxide (NO_(x)) which are emittedfrom an internal combustion engine such as an automobile engine and thelike. Recently, the use of perovskite-type complex oxide also has beenproposed to reduce and purify the nitrogen oxide (NO_(x)) (for example,see Japanese Patent Laid-Open No. 2001-263051 publication).

Meanwhile, particulate matter (particulate) including carbon, soot, andhydrocarbon (HC) as well as the above harmful gases is emitted from aninternal combustion engine such as a diesel engine and the like. Theparticulate matter is alleged to be the leading cause of air pollution,and the harmfulness of the particulate matter contributing tocarcinogenicity and asthma has been singled out. Such particulate mattercan be removed by using a filter and the like so that the particulatematter would be collected and burned there.

So, the use of the above perovskite-type complex oxide itself as acatalyst, or the use of the perovskite-type complex oxide of whichcrystal lattice has Pt or Pd therein as a catalyst have been proposed(for example, see Japanese Patent Laid-Open No. 8-229404 publication andJapanese Patent Laid-Open No. 8-217461 publication).

In order to burn the particulate matter in the air, a high temperatureof 500 to 600° C. is required, and the use of the perovskite-typecomplex oxide or the perovskite-type complex oxide of which crystallattice has Pt or Pd therein as a catalyst is considered to allow thetemperature to burn the particulate matter to be decreased.

However, because the particulate matter is chemically more stable thanthe harmful gases, the catalysts cannot provide sufficient effect todecrease the burning temperature, and inconveniently, the purifyingapparatus needs to be provided with a higher temperature atmosphere orto be of a larger size. Such a higher temperature atmosphere for thepurifying apparatus in turn requires a catalyst which is highly durable,and the purifying apparatus of a larger size causes a disadvantage ofmounting a large apparatus onto a movable body such as automobile.

SUMMARY OF THE INVENTION

The present invention is made to overcome the above disadvantages, andone object of the present invention is to provide an apparatus forremoving particulate matter which is able to decrease a combustiontemperature of the particulate matter.

The inventors of the present invention have carefully studied the reasonwhy the conventional perovskite-type complex oxide or the catalyst ofwhich crystal lattice has Pt or Pd cannot sufficiently decrease thecombustion temperature of the particulate matter. As a result, theinventors of the present invention found that the conventionalperovskite-type complex oxide including an element having a valence of+2 as a metal for B of the general formula ABO₃ cannot provide asufficient oxygen releasing capacity.

The inventors of the present invention have conducted a further studybased on the knowledge above described, and found that perovskite-typecomplex oxide including an element having a valence of +3 as a metal forB of the general formula ABO₃ can provide better oxygen releasingcapacity, which leaded to the present invention.

Therefore, in order to achieve the above object, the present inventionprovides an apparatus for removing particulate matter which burns andremoves particulate matter emitted from an internal combustion engine,comprising a perovskite-type complex oxide which is represented by thegeneral formula ABO₃ where B is a metal having a valence of +3 or more.

An apparatus for removing particulate matter according to the presentinvention comprises a perovskite-type complex oxide which is representedby the general formula ABO₃ where B is a metal having a valence of +3 ormore, and the perovskite-type complex oxide can provide better oxygenreleasing capacity than a conventional perovskite-type complex oxideincluding a metal having a valence of +2 for B.

A perovskite-type complex oxide used in an apparatus for removingparticulate matter according to the present invention preferablyincludes at least one selected from the group consisting of Ti, Zr, Hf,V, Cr, Mo, W, Mn, Fe, Ru, Co, Ni, Cu, Ag, Au as a metal having a valenceof +3 or more for B of the general formula to provide an excellentoxygen releasing capacity.

The perovskite-type complex oxide has an excellent oxygen releasingcapacity as described above, and can burn particulate matter includingcarbon, soot, hydrocarbon (HC) and the like at a temperature which islower than a temperature conventionally required, by taking theadvantage of supporting Pt or Pd.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph to show oxygen releasing capacity of a perovskite-typecomplex oxide which is used in an apparatus for removing particulatematter according to the present invention;

FIG. 2 is a graph to show oxygen releasing capacity of a perovskite-typecomplex oxide which is used in an apparatus for removing particulatematter according to the present invention;

FIG. 3 is a graph to show oxygen releasing capacity of a perovskite-typecomplex oxide which is used in an apparatus for removing particulatematter according to the present invention; and

FIG. 4 is a graph to show oxidization characteristics of a platinumsupporting perovskite-type complex oxide which is used in an apparatusfor removing particulate matter according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, embodiments of the present invention will be explained in detailwith reference to the accompanying drawings. FIGS. 1 to 3 are graphs toshow oxygen releasing capacity of a perovskite-type complex oxide whichis used in an apparatus for removing particulate matter according to thepresent invention, and FIG. 4 is a graph to show oxidizationcharacteristics of a platinum supporting perovskite-type complex oxidewhich is used in an apparatus for removing particulate matter accordingto the present invention.

An apparatus for removing particulate matter of this embodiment burnsand removes particulate matter (particulate) including carbon, soot,hydrocarbon (HC) in exhaust gas emitted from an internal combustionengine of automobile engines and the like, and comprises aperovskite-type complex oxide which is represented by the generalformula ABO₃ where B is a metal having a valence of +3 or more.

The perovskite-type complex oxide may include La, Ba, or Sr as the metalfor A of the general formula. The A may include one metal, or two ormore different metals.

The perovskite-type complex oxide preferably include a metal having avalence of +3 or more for B of the general formula selected from thegroup consisting of Ti, Zr, Hf, V, Cr, Mo, W, Mn, Fe, Ru, Co, Ni, Cu,Ag, and Au. The B may include one metal, or two or more differentmetals, and when B includes two or more different metals, at least oneof the metals should have a valence of +3 or more.

The perovskite-type complex oxide can be synthesized by mixing apredetermined amount of the salt or oxide of a metal for A and apredetermined amount of the salt or oxide of a metal for B, and heatingand firing the mixture. The salt may be nitrate or the like, forexample.

In the apparatus for removing particulate matter of this embodiment, theperovskite-type complex oxide supports a noble metal such as Pt and Pdas an oxidizing catalyst. The oxidizing catalyst may be simply supportedon a surface of the perovskite-type complex oxide, but in this case,while being used at a high temperature, the noble metal tends toconcentrate and its dispersion is decreased, thereby the catalystactivity may deteriorate. Thus, the oxidizing catalyst is preferablytaken in crystal lattice of the perovskite-type complex oxide to besupported therein.

The perovskite-type complex oxide may be preformed in a shape of pellet,honeycomb, or the like to support the oxidizing catalyst, depending on ashape of the apparatus for removing particulate matter.

Now, Examples and Comparative Examples of the present invention will bedescribed below.

EXAMPLE 1

First, in this example, equimolar quantities of lanthanum nitrate andmanganese (III) nitrate, and four-fold molar excess of urea of a metalsalt were dissolved in a small amount of water, and the solution waspoured into a porcelain pot for a primary firing for two hours at 350°C. and further a secondary firing for one hour at 1000° C., whichresulted in a perovskite-type complex oxide represented by LaMn(III)O₃.Next, the temperature of the resulting perovskite-type complex oxide ofthis example was raised from an ambient temperature to 900° C. at therate of 10° C./minute in a vacuum of 1.33×10⁻⁵ Pa, and oxygen releasingcapacity of the oxide was measured. The oxygen releasing capacity wasdetermined, by measuring the oxygen which was desorbed during the aboveraise of temperature as a mass spectrum intensity of a mass-to-chargeratio (m/z)=32 with a mass analyzer. The result is shown in FIG. 1.

COMPARATIVE EXAMPLE 1

First, in this comparative example, a perovskite-type complex oxidewhich is represented by LaMn(II)O₃ was obtained in the same manner as inExample 1 except that manganese (II) nitrate was used instead ofmanganese (III) nitrate. Next, the oxygen releasing capacity of theresulting perovskite-type complex oxide in this comparative example wasmeasured in the same manner as in Example 1. The result is shown in FIG.1.

EXAMPLE 2

First, in this example, equimolar quantities of lanthanum nitrate,manganese (III) nitrate and strontium nitrate, and four-fold molarexcess of urea of a metal salt were dissolved in a small amount ofwater, and the solution was poured into a porcelain pot for a primaryfiring for two hours at 350° C. and further a secondary firing for onehour at 1000° C., which resulted in a perovskite-type complex oxiderepresented by LaSrMn(II)O₃. Next, the oxygen releasing capacity of theresulting perovskite-type complex oxide in this example was measured inthe same manner as in Example 1. The result is shown in FIG. 2.

COMPARATIVE EXAMPLE 2

First, in this comparative example, a perovskite-type complex oxidewhich is represented by LaSrMn(II)O₃ was obtained in the same manner asin Example 2 except that manganese (II) nitrate was used instead ofmanganese (III) nitrate. Next, the oxygen releasing capacity of theresulting perovskite-type complex oxide in this comparative example wasmeasured in the same manner as in Example 1. The result is shown in FIG.2.

EXAMPLE 3

First, in this example, equimolar quantities of lanthanum nitrate andcobalt (III) nitrate, and four-fold molar excess of urea of a metal saltwere dissolved in a small amount of water, and the solution was pouredinto a porcelain pot for a primary firing for two hours at 350° C. andfurther a secondary firing for one hour at 1000° C., which resulted in aperovskite-type complex oxide represented by LaCo(III)O₃. Next, theoxygen releasing capacity of the resulting perovskite-type complex oxidein this example was measured in the same manner as in Example 1. Theresult is shown in FIG. 3.

COMPARATIVE EXAMPLE 3

First, in this comparative example, a perovskite-type complex oxidewhich is represented by LaCo(II)O₃ was obtained in the same manner as inExample 2 except that cobalt (II) nitrate was used instead of cobalt(III) nitrate. Next, the oxygen releasing capacity of the resultingperovskite-type complex oxide in this comparative example was measuredin the same manner as in Example 1. The result is shown in FIG. 3.

FIG. 1 and FIG. 2 clearly show that LaMn(III)O₃ and LaSrMn(III)O₃ havebetter oxygen releasing capacity than LaMn(II)O₃ and LaSrMn(II)O₃ in arange of lower temperatures. Also, FIG. 3 clearly shows that LaCo(III)O₃has better oxygen releasing capacity than LaCo(II)O₃ in the wholemeasured range of temperatures.

EXAMPLE 4

First, in this example, the resulting perovskite-type complex oxide inExample 1 was dispersed in a chloroplatinic acid solution, which wasthen evaporated and dried. The solid after evaporation and drying wassubjected to a firing for two hours at 600° C. in the air for preparinga platinum supporting perovskite-type complex oxide. Next, the resultingplatinum supporting perovskite-type complex oxide in this example wasmixed with carbon black at a weight ratio of 20:1, and the temperatureof the mixture was raised from an ambient temperature to 800° C. at therate of 10° C./minute in an atmospheric environment. The heat flow rateduring the raise of the temperature was measured, and the oxidizationcharacteristics of the oxide was evaluated by comparing the peak heatflow rate to the peak combustion temperature of the carbon black. Theresult is shown in FIG. 4.

EXAMPLE 5

First, in this example, a platinum supporting perovskite-type complexoxide was prepared in the same manner as in Example 4 except that theperovskite-type complex oxide obtained in Example 2 was used. Next, theoxidization characteristics of the resulting platinum supportingperovskite-type complex oxide in this example was evaluated in the samemanner as in Example 4. The result is shown in FIG. 4.

COMPARATIVE EXAMPLE 4

First, in this comparative example, a platinum supportingperovskite-type complex oxide was prepared in the same manner as inExample 4 except that the perovskite-type complex oxide obtained inComparative Example 1 was used. Next, the oxidization characteristics ofthe resulting platinum supporting perovskite-type complex oxide in thiscomparative example was evaluated in the same manner as in Example 4.The result is shown in FIG. 4.

COMPARATIVE EXAMPLE 5

First, in this Comparative Example, a platinum supportingperovskite-type complex oxide was prepared in the same manner as inExample 4 except that the perovskite-type complex oxide obtained inComparative Example 2 was used. Next, the oxidization characteristics ofthe resulting platinum supporting perovskite-type complex oxide obtainedin this Comparative Example was evaluated in the same manner as inExample 4. The result is shown in FIG. 4.

FIG. 4 clearly shows that the platinum supporting LaMn(III)O₃ andLaSrMn(III)O₃ have lower heat flow rates than those of LaMn(II)O₃ andLaSrMn(II)O₃ relative to the peak combustion temperature of carbonblack.

1. An apparatus for removing particulate matter which burns and removesparticulate matter emitted from an internal combustion engine,comprising: a perovskite-type complex oxide which is represented by thegeneral formula ABO₃ where B is a metal having a valence of +3 or more.2. The apparatus for removing particulate matter according to claim 1,wherein the metal having a valence of +3 or more for B of the generalformula comprises at least one metal selected from the group consistingof Ti, Zr, Hf, V, Cr, Mo, W, Mn, Fe, Ru, Co, Ni, Cu, Ag, and Au.
 3. Theapparatus for removing particulate matter according to claim 1, whereinthe perovskite-type complex oxide comprises at least one complex oxideselected from the group consisting of LaMn(III)O₃, LaSrMn(III)O₃, andLaCo(III)O₃.
 4. The apparatus for removing particulate matter accordingto claim 1, wherein the perovskite-type complex oxide supports Pt or Pd.